1. Field of the Invention
The invention relates to domestic appliances which commonly use at least one AC induction drive motor such as clothes washers, dishwashers, clothes dryers, trash compactors, food refrigerators, heat pumps and air conditioners. In particular the invention relates to (1) a motor phase monitoring circuit means for generating one independent motor phase sample during each line voltage half cycle and (2) appropriate appliance microcomputer program routines which use the above phase samples to infer motor output torque for the purpose of controlling operation of the appliance.
2. Description of the Prior Art
A power factor control system for AC induction motors is disclosed in U.S. Pat. No. 4,052,648 which samples line voltage and current through the motor and decreases power input to the motor in proportion to the detected phase displacement between current and voltage thereby providing less power to the motor when the motor is lightly loaded.
An electronic method and apparatus for monitoring motor torque is disclosed in U.S. Pat. No. 3,600,657 which employs a current sensitive pickup device in combination with a zero crossing detector and a pulse generator circuit for producing an analog signal which is proportional to the motor torque and which is employed to control a relay to start and stop the motor.
A circuit for monitoring the mechanical power from an induction motor and for detecting excessive heat exchanger icing is disclosed in U.S. Pat. No. 4,123,792 wherein a circuit is used in conjunction with a small resistor wired in series with the outdoor evaporator fan motor of a heat pump to develop a signal corresponding to Icos.theta. which is substantially proportional to the mechanical output of the motor. The signal is averaged for a period of several seconds by an RC integrating circuit and the averaged signal is compared to a reference load set point which must be individually adjusted for each fan motor during installation of each heat exchanger.
The present electromechanical pressure switches used for clothes washer water-level control permit user selection and control of the water fill by adjusting a control knob or lever switch which is connected by mechanical linkage to an eccentric cam which prebiases the diaphragm of the pressure switch mechanism. The present system affords the possibility of considerable operator error either by wasting hot water or by allowing all drive train components to be damaged by torque overloads due to insufficient water in the wash bath. Abrasion damage to clothes items can also result from insufficient water in the wash bath. Control systems which eliminate this problem by not allowing direct user selection or control of the water level and by instead controlling the water fill in response to some machine condition are called automatic water level controls.
Prior art clothes washer automatic water level controls are disclosed in U.S. Pat. Nos. 3,030,790; 3,359,766; 3,478,373; 3,497,884 and 3,508,287, these controls respond respectively, to torque transmitted through the wash bath from the agitator to the spin basket, wash load torque manifested as fluid pressure in a hydrostatic transmission, water flow due to clothes rollover in the wash bath, restraining torque exerted on the agitator and motion of the spin basket relative to the tub due to agitator action.
An electronic liquid level monitoring system which provides a quantitative analog-type measurement of water level in a digital format is disclosed in U.S. Pat. No. 4,201,240. A mechanical device oscillates within a coil to provide signals which are counted and a calculated multiple of the count is compared with an electronically stored table corresponding to predetermined liquid levels and the results of the comparison is utilized to initiate control functions for operating the washing machine by means of a microcomputer.
Prior art dishwasher water fill volume has generally been controlled by electrical actuation of the solenoid of a fill valve for a fixed time period, typically 120 seconds, and metering the water inlet flow rate with a flow washer having one or more orifices that are size responsive to the installation water pressure. Overflow failures are prevented by a separate float switch wired in series with the fill valve solenoid. A preset factory calibrated dishwasher fill volume must assume simultaneous worst case conditions of fast pump, full dish loading, high sudsing detergent and high line voltage to guarantee that all units will always operate with sufficient water to avoid pump starvation. This often results in some wasted hot water when any or all of the above worst case conditions are not present. Dishwasher controls which automatically terminate the water fill as soon as sufficient water is present in the dishwashing system to allow smooth water pumping at a maximum flow rate with no water starvation under a wide variety of operating conditions are called automatic water level controls.
A dishwasher automatic water level control is disclosed in U.S. Pat. No. 3,415,261 wherein a pressure responsive switch in the lower sump area is used to detect when sufficient water is present in the dishwashing system to achieve a full pumping water pressure and terminate the water fill. Elevated air holes at the pump water inlet area result in the pump drawing partly air and cavitating until the sump water reaches the proper fill height.
A microprocessor based control circuit for washing appliances such as dishwashers and clothes washers is disclosed in U.S. Pat. No. 4,241,400 wherein a drain feedback switch is mechanically linked to a hinged diverter valve in the pump water flow path to detect when substantially all of the water has been discharged into the drain line. The electrical state of the drain feedback switch is input to the microprocessor to save or reallocate machine cycle time and facilitate detection of various drain fault conditions such as the failure to drain, slow drain or a plugged drain.
U.S. Pat. No. 3,777,232 discloses a circuit wherein the start winding of a motor is removed from the circuit on the basis of a phase difference between the main winding current and the applied voltage.